// WebGL - 3D Camera Look At Heads
// from https://webglfundamentals.org/webgl/webgl-3d-camera-look-at-heads.html


"use strict";

function main() {
    // Get A WebGL context
    /** @type {HTMLCanvasElement} */
    var canvas = document.querySelector("#canvas");
    var gl = canvas.getContext("webgl");
    if (!gl) {
        return;
    }

    // setup GLSL program
    var program = webglUtils.createProgramFromScripts(gl, ["vertex-shader-3d", "fragment-shader-3d"]);
    gl.useProgram(program);

    // look up where the vertex data needs to go.
    var positionLocation = gl.getAttribLocation(program, "a_position");
    var colorLocation = gl.getAttribLocation(program, "a_color");

    // lookup uniforms
    var matrixLocation = gl.getUniformLocation(program, "u_matrix");

    // Create a buffer to put positions in
    var positionBuffer = gl.createBuffer();
    // Bind it to ARRAY_BUFFER (think of it as ARRAY_BUFFER = positionBuffer)
    gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);
    // Put geometry data into buffer
    var numElements = setGeometry(gl);

    // Create a buffer to put colors in
    var colorBuffer = gl.createBuffer();
    // Bind it to ARRAY_BUFFER (think of it as ARRAY_BUFFER = colorBuffer)
    gl.bindBuffer(gl.ARRAY_BUFFER, colorBuffer);
    // Put geometry data into buffer
    setColors(gl);

    function radToDeg(r) {
        return r * 180 / Math.PI;
    }

    function degToRad(d) {
        return d * Math.PI / 180;
    }

    var target = [0, 200, 300];
    var targetAngleRadians = 0;
    var targetRadius = 300;
    var fieldOfViewRadians = degToRad(60);

    // drawScene();

    // Setup a ui.
    // webglLessonsUI.setupSlider("#targetAngle", { value: radToDeg(targetAngleRadians), slide: updateTargetAngle, min: -360, max: 360 });
    // webglLessonsUI.setupSlider("#targetHeight", { value: target[1], slide: updateTargetHeight, min: 50, max: 300 });

    function updateTargetAngle(event, ui) {
        targetAngleRadians = degToRad(ui.value);
        target[0] = Math.sin(targetAngleRadians) * targetRadius;
        target[2] = Math.cos(targetAngleRadians) * targetRadius;
        drawScene();
    }

    function updateTargetHeight(event, ui) {
        target[1] = ui.value;
        drawScene();
    }

    var then = 0;

    requestAnimationFrame(drawScene);

    // Draw the scene.
    function drawScene(now) {
        var numFs = 5;
        var radius = 600;

        // Convert to seconds
        now *= 0.001;
        // Subtract the previous time from the current time
        var deltaTime = now - then;
        // Remember the current time for the next frame.
        then = now;

        // Every frame increase the rotation a little.
        targetAngleRadians += 1.2 * deltaTime;
        target[0] = Math.sin(targetAngleRadians) * targetRadius;
        target[2] = Math.cos(targetAngleRadians) * targetRadius;

        webglUtils.resizeCanvasToDisplaySize(gl.canvas);

        // Tell WebGL how to convert from clip space to pixels
        gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);

        // Clear the canvas AND the depth buffer.
        gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

        // Turn on culling. By default backfacing triangles
        // will be culled.
        gl.enable(gl.CULL_FACE);

        // Enable the depth buffer
        gl.enable(gl.DEPTH_TEST);

        // Tell it to use our program (pair of shaders)
        gl.useProgram(program);

        // Turn on the position attribute
        gl.enableVertexAttribArray(positionLocation);

        // Bind the position buffer.
        gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);

        // Tell the position attribute how to get data out of positionBuffer (ARRAY_BUFFER)
        var size = 3;          // 3 components per iteration
        var type = gl.FLOAT;   // the data is 32bit floats
        var normalize = false; // don't normalize the data
        var stride = 0;        // 0 = move forward size * sizeof(type) each iteration to get the next position
        var offset = 0;        // start at the beginning of the buffer
        gl.vertexAttribPointer(
            positionLocation, size, type, normalize, stride, offset);

        // Turn on the color attribute
        gl.enableVertexAttribArray(colorLocation);

        // Bind the color buffer.
        gl.bindBuffer(gl.ARRAY_BUFFER, colorBuffer);

        // Tell the attribute how to get data out of colorBuffer (ARRAY_BUFFER)
        var size = 3;                 // 3 components per iteration
        var type = gl.UNSIGNED_BYTE;  // the data is 8bit unsigned values
        var normalize = true;         // normalize the data (convert from 0-255 to 0-1)
        var stride = 0;               // 0 = move forward size * sizeof(type) each iteration to get the next position
        var offset = 0;               // start at the beginning of the buffer
        gl.vertexAttribPointer(
            colorLocation, size, type, normalize, stride, offset);

        // Compute the projection matrix
        var aspect = gl.canvas.clientWidth / gl.canvas.clientHeight;
        var zNear = 1;
        var zFar = 3000;
        var projectionMatrix = m4.perspective(fieldOfViewRadians, aspect, zNear, zFar);

        var cameraTarget = [0, -100, 0];
        var cameraPosition = [500, 300, 500];
        var up = [0, 1, 0];

        // Compute the camera's matrix using look at.
        var cameraMatrix = m4.lookAt(cameraPosition, cameraTarget, up);

        // Make a view matrix from the camera matrix.
        var viewMatrix = m4.inverse(cameraMatrix);

        // create a viewProjection matrix. This will both apply perspective
        // AND move the world so that the camera is effectively the origin
        var viewProjectionMatrix = m4.multiply(projectionMatrix, viewMatrix);

        // Draw heads in a grid
        var deep = 5;
        var across = 5;
        for (var zz = 0; zz < deep; ++zz) {
            var v = zz / (deep - 1);
            var z = (v - .5) * deep * 150;
            for (var xx = 0; xx < across; ++xx) {
                var u = xx / (across - 1);
                var x = (u - .5) * across * 150;
                var matrix = m4.lookAt([x, 0, z], target, up);
                drawHead(matrix, viewProjectionMatrix, matrixLocation, numElements);
            }
        }
        var matrix2 = m4.lookAt([target[0], target[1], target[2]], [0, 100, 0], up);
        drawHead(matrix2, viewProjectionMatrix, matrixLocation, numElements);

        requestAnimationFrame(drawScene)
    }

    function drawHead(matrix, viewProjectionMatrix, matrixLocation, numElements) {
        // multiply that with the viewProjecitonMatrix
        matrix = m4.multiply(viewProjectionMatrix, matrix);

        // Set the matrix.
        gl.uniformMatrix4fv(matrixLocation, false, matrix);

        // Draw the geometry.
        var primitiveType = gl.TRIANGLES;
        var offset = 0;
        gl.drawArrays(gl.TRIANGLES, 0, numElements);
    }
}

function subtractVectors(a, b) {
    return [a[0] - b[0], a[1] - b[1], a[2] - b[2]];
}

function normalize(v) {
    var length = Math.sqrt(v[0] * v[0] + v[1] * v[1] + v[2] * v[2]);
    // make sure we don't divide by 0.
    if (length > 0.00001) {
        return [v[0] / length, v[1] / length, v[2] / length];
    } else {
        return [0, 0, 0];
    }
}

function cross(a, b) {
    return [a[1] * b[2] - a[2] * b[1],
    a[2] * b[0] - a[0] * b[2],
    a[0] * b[1] - a[1] * b[0]];
}



var m4 = {

    lookAt: function (cameraPosition, target, up) {
        var zAxis = normalize(
            subtractVectors(cameraPosition, target));
        var xAxis = normalize(cross(up, zAxis));
        var yAxis = normalize(cross(zAxis, xAxis));

        return [
            xAxis[0], xAxis[1], xAxis[2], 0,
            yAxis[0], yAxis[1], yAxis[2], 0,
            zAxis[0], zAxis[1], zAxis[2], 0,
            cameraPosition[0],
            cameraPosition[1],
            cameraPosition[2],
            1,
        ];
    },

    perspective: function (fieldOfViewInRadians, aspect, near, far) {
        var f = Math.tan(Math.PI * 0.5 - 0.5 * fieldOfViewInRadians);
        var rangeInv = 1.0 / (near - far);

        return [
            f / aspect, 0, 0, 0,
            0, f, 0, 0,
            0, 0, (near + far) * rangeInv, -1,
            0, 0, near * far * rangeInv * 2, 0
        ];
    },

    projection: function (width, height, depth) {
        // Note: This matrix flips the Y axis so 0 is at the top.
        return [
            2 / width, 0, 0, 0,
            0, -2 / height, 0, 0,
            0, 0, 2 / depth, 0,
            -1, 1, 0, 1,
        ];
    },

    multiply: function (a, b) {
        var a00 = a[0 * 4 + 0];
        var a01 = a[0 * 4 + 1];
        var a02 = a[0 * 4 + 2];
        var a03 = a[0 * 4 + 3];
        var a10 = a[1 * 4 + 0];
        var a11 = a[1 * 4 + 1];
        var a12 = a[1 * 4 + 2];
        var a13 = a[1 * 4 + 3];
        var a20 = a[2 * 4 + 0];
        var a21 = a[2 * 4 + 1];
        var a22 = a[2 * 4 + 2];
        var a23 = a[2 * 4 + 3];
        var a30 = a[3 * 4 + 0];
        var a31 = a[3 * 4 + 1];
        var a32 = a[3 * 4 + 2];
        var a33 = a[3 * 4 + 3];
        var b00 = b[0 * 4 + 0];
        var b01 = b[0 * 4 + 1];
        var b02 = b[0 * 4 + 2];
        var b03 = b[0 * 4 + 3];
        var b10 = b[1 * 4 + 0];
        var b11 = b[1 * 4 + 1];
        var b12 = b[1 * 4 + 2];
        var b13 = b[1 * 4 + 3];
        var b20 = b[2 * 4 + 0];
        var b21 = b[2 * 4 + 1];
        var b22 = b[2 * 4 + 2];
        var b23 = b[2 * 4 + 3];
        var b30 = b[3 * 4 + 0];
        var b31 = b[3 * 4 + 1];
        var b32 = b[3 * 4 + 2];
        var b33 = b[3 * 4 + 3];
        return [
            b00 * a00 + b01 * a10 + b02 * a20 + b03 * a30,
            b00 * a01 + b01 * a11 + b02 * a21 + b03 * a31,
            b00 * a02 + b01 * a12 + b02 * a22 + b03 * a32,
            b00 * a03 + b01 * a13 + b02 * a23 + b03 * a33,
            b10 * a00 + b11 * a10 + b12 * a20 + b13 * a30,
            b10 * a01 + b11 * a11 + b12 * a21 + b13 * a31,
            b10 * a02 + b11 * a12 + b12 * a22 + b13 * a32,
            b10 * a03 + b11 * a13 + b12 * a23 + b13 * a33,
            b20 * a00 + b21 * a10 + b22 * a20 + b23 * a30,
            b20 * a01 + b21 * a11 + b22 * a21 + b23 * a31,
            b20 * a02 + b21 * a12 + b22 * a22 + b23 * a32,
            b20 * a03 + b21 * a13 + b22 * a23 + b23 * a33,
            b30 * a00 + b31 * a10 + b32 * a20 + b33 * a30,
            b30 * a01 + b31 * a11 + b32 * a21 + b33 * a31,
            b30 * a02 + b31 * a12 + b32 * a22 + b33 * a32,
            b30 * a03 + b31 * a13 + b32 * a23 + b33 * a33,
        ];
    },

    translation: function (tx, ty, tz) {
        return [
            1, 0, 0, 0,
            0, 1, 0, 0,
            0, 0, 1, 0,
            tx, ty, tz, 1,
        ];
    },

    xRotation: function (angleInRadians) {
        var c = Math.cos(angleInRadians);
        var s = Math.sin(angleInRadians);

        return [
            1, 0, 0, 0,
            0, c, s, 0,
            0, -s, c, 0,
            0, 0, 0, 1,
        ];
    },

    yRotation: function (angleInRadians) {
        var c = Math.cos(angleInRadians);
        var s = Math.sin(angleInRadians);

        return [
            c, 0, -s, 0,
            0, 1, 0, 0,
            s, 0, c, 0,
            0, 0, 0, 1,
        ];
    },

    zRotation: function (angleInRadians) {
        var c = Math.cos(angleInRadians);
        var s = Math.sin(angleInRadians);

        return [
            c, s, 0, 0,
            -s, c, 0, 0,
            0, 0, 1, 0,
            0, 0, 0, 1,
        ];
    },

    scaling: function (sx, sy, sz) {
        return [
            sx, 0, 0, 0,
            0, sy, 0, 0,
            0, 0, sz, 0,
            0, 0, 0, 1,
        ];
    },

    translate: function (m, tx, ty, tz) {
        return m4.multiply(m, m4.translation(tx, ty, tz));
    },

    xRotate: function (m, angleInRadians) {
        return m4.multiply(m, m4.xRotation(angleInRadians));
    },

    yRotate: function (m, angleInRadians) {
        return m4.multiply(m, m4.yRotation(angleInRadians));
    },

    zRotate: function (m, angleInRadians) {
        return m4.multiply(m, m4.zRotation(angleInRadians));
    },

    scale: function (m, sx, sy, sz) {
        return m4.multiply(m, m4.scaling(sx, sy, sz));
    },

    inverse: function (m) {
        var m00 = m[0 * 4 + 0];
        var m01 = m[0 * 4 + 1];
        var m02 = m[0 * 4 + 2];
        var m03 = m[0 * 4 + 3];
        var m10 = m[1 * 4 + 0];
        var m11 = m[1 * 4 + 1];
        var m12 = m[1 * 4 + 2];
        var m13 = m[1 * 4 + 3];
        var m20 = m[2 * 4 + 0];
        var m21 = m[2 * 4 + 1];
        var m22 = m[2 * 4 + 2];
        var m23 = m[2 * 4 + 3];
        var m30 = m[3 * 4 + 0];
        var m31 = m[3 * 4 + 1];
        var m32 = m[3 * 4 + 2];
        var m33 = m[3 * 4 + 3];
        var tmp_0 = m22 * m33;
        var tmp_1 = m32 * m23;
        var tmp_2 = m12 * m33;
        var tmp_3 = m32 * m13;
        var tmp_4 = m12 * m23;
        var tmp_5 = m22 * m13;
        var tmp_6 = m02 * m33;
        var tmp_7 = m32 * m03;
        var tmp_8 = m02 * m23;
        var tmp_9 = m22 * m03;
        var tmp_10 = m02 * m13;
        var tmp_11 = m12 * m03;
        var tmp_12 = m20 * m31;
        var tmp_13 = m30 * m21;
        var tmp_14 = m10 * m31;
        var tmp_15 = m30 * m11;
        var tmp_16 = m10 * m21;
        var tmp_17 = m20 * m11;
        var tmp_18 = m00 * m31;
        var tmp_19 = m30 * m01;
        var tmp_20 = m00 * m21;
        var tmp_21 = m20 * m01;
        var tmp_22 = m00 * m11;
        var tmp_23 = m10 * m01;

        var t0 = (tmp_0 * m11 + tmp_3 * m21 + tmp_4 * m31) -
            (tmp_1 * m11 + tmp_2 * m21 + tmp_5 * m31);
        var t1 = (tmp_1 * m01 + tmp_6 * m21 + tmp_9 * m31) -
            (tmp_0 * m01 + tmp_7 * m21 + tmp_8 * m31);
        var t2 = (tmp_2 * m01 + tmp_7 * m11 + tmp_10 * m31) -
            (tmp_3 * m01 + tmp_6 * m11 + tmp_11 * m31);
        var t3 = (tmp_5 * m01 + tmp_8 * m11 + tmp_11 * m21) -
            (tmp_4 * m01 + tmp_9 * m11 + tmp_10 * m21);

        var d = 1.0 / (m00 * t0 + m10 * t1 + m20 * t2 + m30 * t3);

        return [
            d * t0,
            d * t1,
            d * t2,
            d * t3,
            d * ((tmp_1 * m10 + tmp_2 * m20 + tmp_5 * m30) -
                (tmp_0 * m10 + tmp_3 * m20 + tmp_4 * m30)),
            d * ((tmp_0 * m00 + tmp_7 * m20 + tmp_8 * m30) -
                (tmp_1 * m00 + tmp_6 * m20 + tmp_9 * m30)),
            d * ((tmp_3 * m00 + tmp_6 * m10 + tmp_11 * m30) -
                (tmp_2 * m00 + tmp_7 * m10 + tmp_10 * m30)),
            d * ((tmp_4 * m00 + tmp_9 * m10 + tmp_10 * m20) -
                (tmp_5 * m00 + tmp_8 * m10 + tmp_11 * m20)),
            d * ((tmp_12 * m13 + tmp_15 * m23 + tmp_16 * m33) -
                (tmp_13 * m13 + tmp_14 * m23 + tmp_17 * m33)),
            d * ((tmp_13 * m03 + tmp_18 * m23 + tmp_21 * m33) -
                (tmp_12 * m03 + tmp_19 * m23 + tmp_20 * m33)),
            d * ((tmp_14 * m03 + tmp_19 * m13 + tmp_22 * m33) -
                (tmp_15 * m03 + tmp_18 * m13 + tmp_23 * m33)),
            d * ((tmp_17 * m03 + tmp_20 * m13 + tmp_23 * m23) -
                (tmp_16 * m03 + tmp_21 * m13 + tmp_22 * m23)),
            d * ((tmp_14 * m22 + tmp_17 * m32 + tmp_13 * m12) -
                (tmp_16 * m32 + tmp_12 * m12 + tmp_15 * m22)),
            d * ((tmp_20 * m32 + tmp_12 * m02 + tmp_19 * m22) -
                (tmp_18 * m22 + tmp_21 * m32 + tmp_13 * m02)),
            d * ((tmp_18 * m12 + tmp_23 * m32 + tmp_15 * m02) -
                (tmp_22 * m32 + tmp_14 * m02 + tmp_19 * m12)),
            d * ((tmp_22 * m22 + tmp_16 * m02 + tmp_21 * m12) -
                (tmp_20 * m12 + tmp_23 * m22 + tmp_17 * m02))
        ];
    },

    vectorMultiply: function (v, m) {
        var dst = [];
        for (var i = 0; i < 4; ++i) {
            dst[i] = 0.0;
            for (var j = 0; j < 4; ++j) {
                dst[i] += v[j] * m[j * 4 + i];
            }
        }
        return dst;
    },

};


// Fill the buffer with the values that define a letter 'F'.
function setGeometry(gl) {
    var positions = new Float32Array(HeadData.positions);
    var matrix = m4.multiply(m4.scaling(6, 6, 6), m4.yRotation(Math.PI));
    for (var ii = 0; ii < positions.length; ii += 3) {
        var vector = m4.vectorMultiply([positions[ii + 0], positions[ii + 1], positions[ii + 2], 1], matrix);
        positions[ii + 0] = vector[0];
        positions[ii + 1] = vector[1];
        positions[ii + 2] = vector[2];
    }

    gl.bufferData(gl.ARRAY_BUFFER, positions, gl.STATIC_DRAW);
    return positions.length / 3;
}

// Fill the buffer with colors for the 'F'.
function setColors(gl, numElements) {
    var normals = HeadData.normals;
    var colors = new Uint8Array(normals.length);
    var offset = 0;
    for (var ii = 0; ii < colors.length; ii += 3) {
        for (var jj = 0; jj < 3; ++jj) {
            colors[offset] = (normals[offset] * 0.5 + 0.5) * 255;
            ++offset;
        }
    }
    gl.bufferData(
        gl.ARRAY_BUFFER, colors, gl.STATIC_DRAW);
}
main();
